Evaluating the Potential Impact of Climate Change on the Hydrology of Ribb Catchment, Blue Nile Basin, Ethiopia

Abstract

Varies scientific findings indicate there is climate change which affects a given hydrology and, hence, water availability. To quantify its impact on the specific catchment scale since spatial and temporal variability of climate change impact, this study was carried out at Ribb catchment, Blue Nile Basin Ethiopia. Bias corrected Regional Climate Model (RCM) projection data set for Nile Basin studies at Representative Concentration Pathway (RCPs) (RCP4.5 and RCP8.5) were used for trend analysis and future stream flow generation. It were analyzed for three time horizons on 2020s (2011-2040), 2050s (2041-2070), 2080s (2071-2098). A baseline period (1976-2005) was used as a reference. Trends of future temperature and precipitation change were checked by Mann-Kendall trend test. SWAT was calibrated (R2=0.83 and NSE=0.74) and validated (R2=0.72 and NSE=0.71). Mean annual minimum temperature is found to increase by 2.45 0c at RCP4.5 and 4.64 0c at RCP8.5 scenarios and maximum temperature could increase by 2.41 0c and 5.15 0c at RCP4.5 and RCP8.5 scenarios, respectively, on 2080s. Mean monthly maximum and minimum temperature also showed increasing trend. The highest increase in maximum temperature was found in July whereas the maximum increase in minimum temperature in January. Average monthly and annual precipitation changes vary in magnitude but consistent trend was not found. As a result, mean annual stream flow could potentially reduce from 42.78m3/s to 40.24m3/s and from 42.78m3/s to 37.58m3/s on RCP4.5 and RCP8.5 scenarios, respectively, on 2080s. On monthly time scale, decreases in stream flow were found from March to August whereas slight increase from September to February. With respect to individual months, June flows were found to have maximum impact in both scenarios (63.3% at RCP8.5 and 55.45% at RCP4.5 scenarios). The least impacted month was August based on RCP8.5 scenario which is decreased by 6.64 % and April based on RCP4.5 scenario which is reduced by 1.21%. Looking at total volume, July showed a maximum decrease on both scenarios which is reduced by 21.08 m3/s at RCP4.5 scenario and 51.22 m3/s at RCP8.5 scenario. Maximum increase found in October with 10.31m3/s and 11.26m3/s at RCP4.5 and RCP8.5 scenarios respectively. Besides, a potential decrease at seasonal stream flow was shown in summer and spring whereas may increase slight during autumn and winter. Future stream flow of Ribb River is decreased annually and monthly since increased on future temperature and reduced of rainfall.